Leica R Lenses: Understanding CamsLeica R lenses are 35mm manual focus lenses that fit on Leica R SLR bodies. Most the lenses can be used on any Leica reflex camera body in a non-metered mode (they physically fit onto the body). There are different designations that denote the lenses cams, or cam-coupling, which is how meter-coupling is carried out. So in order for the lens aperture information to make it to the camera for proper metering, you must choose the appropriate lens and camera combination.
|close up of the 3rd cam|
A '3rd-cam' or 'R-only cam' is for R3 and later models. This lens does not have the 1st or 2nd cam (the chrome bars) at all. It only has the 3rd cam (the black tiered cam) located in between the lens mount and the rear element. These lenses also have a slightly different mount shape that prevents it from fitting on earlier camera models (Leicaflex).
|ROM (with 3rd cam)|